Magnetic field sensors and method for determining position and orientation of a magnet

ABSTRACT

A magnetic field sensor for determining a position of a magnet, the position identified by one or more position variables can include: one or more magnetic field sensing element operable to generate one or more magnetic field measurements of the magnet and an associated one or more measured magnetic field variable values; a first module for identifying calculated magnetic field variable values associated with a plurality of positions of the magnet; a second module operable to perform an optimization process to determine a value of a distance function, the distance function using the one or more measured magnetic field variable values and the calculated magnetic field variable values; and a third module operable to determine the position of the magnet by associating the value of the distance function with corresponding values of the one or more position variables. A complimentary method can be used in the magnetic field sensor.

CROSS REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

This invention relates generally to magnetic field sensors and methodsused in magnetic field sensors and, more particularly, to magnetic fieldsensors and methods used in magnetic field sensors that can identify aposition of a magnet in space.

BACKGROUND

Magnetic field sensors employ a variety of types of magnetic fieldsensing elements, for example, Hall effect elements andmagnetoresistance elements, often coupled to a variety of electronics,all disposed over a common substrate. A magnetic field sensing element(and a magnetic field sensor) can be characterized by a variety ofperformance characteristics, one of which is a sensitivity, which can beexpressed in terms of an output signal amplitude versus a magnetic fieldto which the magnetic field sensing element is exposed.

Some magnetic field sensors can detect a linear motion of a targetobject. Some other magnetic field sensors can detect a rotation of atarget object.

SUMMARY

It is appreciated herein that there are many applications where thegeometry and magnetization of a magnet may be known but the magnet'sposition and/or orientation may be unknown. Non-limiting examples ofsuch applications include: (1) “slide-by” applications, where a sensedmagnet undergoes 1-dimensional (1D) linear movement; (2) “all gear”applications where a sensed magnet undergoes 2-dimensional (2D)movement; and (3) end-of-shaft or side-shaft angle sensing applicationswhere a magnet undergoes a rotation. More generally, the sensed magnetcan undergo movement with one, two, three, four, five, or six degrees offreedom.

Described herein are systems and methods to determine theposition/orientation of a magnet using actual measurements taken of amagnetic field resulting from the magnet, calculated (i.e., predicted)measurements of the magnetic field based on a mathematical model of themagnet, and a technique that seeks to minimize a numerical distancebetween the actual and calculated magnetic field measurements. In someembodiments, the magnet position/orientation is determined by finding aglobal minimum of a distance function that calculates a distance betweenactual and calculated magnetic field measurements. In some embodiments,the distance function calculates a mathematical norm between the actualand calculated measurements. In certain embodiments, a steepest descenttechnique may be used to determine values of position/orientation thatreduce the distance function. In some embodiments, techniques may beused to avoid becoming “stuck” in a local minimum when seeking tominimize the distance function.

In many embodiments, position/orientation can be determined for a magnethaving an arbitrary geometry and/or arbitrary magnetization directionand distribution. In some embodiments, position/orientation can bedetermined for multiple magnets, each of which may move independentlyfrom the others.

In particular embodiments, actual magnetic field measurements may betaken as absolute field measurements. In other embodiments, actualmagnetic field measurements be taken as differential field measurements(e.g., in applications where external field perturbation immunity isrequired). In some embodiments, actual magnetic field measurements maybe taken as magnetic field angle measurements. In some embodiments,actual magnetic field measurements may be taken using one or moremagnetic field sensing elements provided as Hall effect elements(vertical or planar) or magnetoresistance elements.

In some embodiments, multiple magnetic field sensing elements may beused to allow for unicity of the determined magnet position/orientation.The magnetic field sensing elements may be oriented along multipledirections. Location and position of the magnetic field sensing elementsmay be selected based on upon the application. Multiple measurements maybe taken from the magnetic field sensing elements.

In accordance with an example useful for understanding an aspect of thepresent invention, a method of determining a position of a magnet, theposition identified by one or more position variables, the includes:generating one or more magnetic field measurements of the magnet and anassociated one or more measured magnetic field variable values using oneor more magnetic field sensing elements; identifying calculated magneticfield variable values associated with a plurality of positions of themagnet; performing an optimization process to determine a value of adistance function, the distance function using the one or more measuredmagnetic field variable values and the calculated magnetic fieldvariable values; and determining the position of the magnet byassociating the value of the distance function with corresponding valuesof the one or more position variables.

In accordance with another example useful for understanding anotheraspect of the present invention, a magnetic field sensor for determininga position of a magnet, the position identified by one or more positionvariables, the magnetic field sensor includes: a first module foridentifying calculated magnetic field variable values associated with aplurality of positions of the magnet; a second module operable toperform an optimization process to determine a value of a distancefunction, the distance function using the one or more measured magneticfield variable values and the calculated magnetic field variable values;and a third module operable to determine the position of the magnet byassociating the value of the distance function with corresponding valuesof the one or more position variables.

In accordance with another example useful for understanding anotheraspect of the present invention, a magnetic field sensor for determininga position of a magnet, the position identified by one or more positionvariables, the magnetic field sensor includes: means for generating oneor more magnetic field measurements of the magnet and an associated oneor more measured magnetic field variable values using one or moremagnetic field sensing elements; means for identifying calculatedmagnetic field variable values associated with a plurality of positionsof the magnet; means for performing an optimization process to determinea value of a distance function, the distance function using the one ormore measured magnetic field variable values and the calculated magneticfield variable values; and means for determining the position of themagnet by associating the value of the distance function withcorresponding values of the one or more position variables.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features may be more fully understood from the followingdescription of the drawings in which:

FIG. 1 is an isometric view of an illustrative system having a magneticfield sensor proximate to a magnet, in accordance with an end of shaftembodiment, with magnet movement along one axis and rotation about oneaxis;

FIG. 1A is a top view of the system of FIG. 1;

FIG. 1B is a side view of the system of FIG. 1;

FIG. 1C is a diagram showing an illustrative arrangement of magneticfield sensing elements that may be used in some embodiments of themagnetic field sensor of FIGS. 1-1B;

FIG. 2A is a side view of illustrative system having a magnetic fieldsensor proximate to a magnet, with magnet movement along two orthogonalaxes;

FIG. 2B is a side view of the system of FIG. 2A;

FIG. 2C is a diagram showing an illustrative arrangement of magneticfield sensing elements that may be used in some embodiments of themagnetic field sensor of FIGS. 2A and 2B;

FIG. 3 is a block diagram of a magnetic field sensor, for example, inaccordance with some embodiments;

FIGS. 4, 4A, 4B, and 5 are flow diagrams illustrating processing thatmay occur within a magnetic field sensor, in accordance with someembodiments.

FIG. 6 is a block diagram showing an illustrative generalized magnetwith an arbitrary shape; and

FIG. 7 is a graph showing an illustrative distance function.

The drawings are not necessarily to scale, or inclusive of all elementsof a system, emphasis instead generally being placed upon illustratingthe concepts, structures, and techniques sought to be protected herein.

DETAILED DESCRIPTION

As used herein, the term “magnetic field sensing element” is used todescribe a variety of electronic elements that can sense a magneticfield. The magnetic field sensing element can be, but is not limited to,a Hall effect element, a magnetoresistance element, or amagnetotransistor. There are different types of Hall effect elements,for example, a planar Hall element, a vertical Hall element, and aCircular Vertical Hall (CVH) element. There are also different types ofmagnetoresistance elements, for example, a semiconductormagnetoresistance element such as Indium Antimonide (InSb), a giantmagnetoresistance (GMR) element, for example, a spin valve, ananisotropic magnetoresistance element (AMR), a tunnelingmagnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ).The magnetic field sensing element might be a single element or,alternatively, might include two or more magnetic field sensing elementsarranged in various configurations, e.g., a half bridge or full(Wheatstone) bridge. Depending on the device type and other applicationrequirements, the magnetic field sensing element might be a device madeof a type IV semiconductor material such as Silicon (Si) or Germanium(Ge), or a type III-V semiconductor material like Gallium-Arsenide(GaAs) or an Indium compound, e.g., Indium-Antimonide (InSb).

Some of the above-described magnetic field sensing elements tend to havean axis of maximum sensitivity parallel to a substrate that supports themagnetic field sensing element, and others of the above-describedmagnetic field sensing elements tend to have an axis of maximumsensitivity perpendicular to a substrate that supports the magneticfield sensing element. In particular, planar Hall elements tend to haveaxes of sensitivity perpendicular to a substrate, while metal based ormetallic magnetoresistance elements (e.g., GMR, TMR, AMR) and verticalHall elements tend to have axes of sensitivity parallel to a substrate.

As used herein, the term “magnetic field sensor” is used to describe acircuit that uses a magnetic field sensing element, generally incombination with other circuits. Magnetic field sensors are used in avariety of applications, including, but not limited to, an angle sensorthat senses an angle of a direction of a magnetic field, a currentsensor that senses a magnetic field generated by a current carried by acurrent-carrying conductor, a magnetic switch that senses the proximityof a ferromagnetic object, a rotation detector that senses passingferromagnetic articles, for example, magnetic domains of a ring magnetor a ferromagnetic target (e.g., gear teeth) where the magnetic fieldsensor is used in combination with a back bias or other magnet, and amagnetic field sensor that senses a magnetic field density of a magneticfield.

As used herein below, the term “magnet” is used to describe a mechanicalstructure having permanent magnetism, relative movement of which issensed by a magnetic field sensor. Thus, either the magnet or themagnetic field sensor, or both, can move relative to each other.However, discussion below refers only to magnet position.

As used herein, the terms “position” and “location” of a magnet refer toa quantified geometric state of the magnet described along one, two, orthree axes and/or described as rotations about the one, two, or threeaxes. Thus, the terms “position” and “location” of a magnet refer to aquantified geometric state of the magnet described with up to sixdegrees of freedom. The up to six degrees of freedom are described as“position variables” (e.g., a six dimension position variable vector)herein. The position variables can have values, described herein asvalues of “position variable values” or “values of position variables.”The position variable values can be stationary or can change with time.There can be any number of position variable values, for any number ofpositions of the magnet at the point (or points) in space.

Similarly, magnetic fields of a magnet at a point in space can bedescribed by “magnetic field variables” (e.g., a three dimensionmagnetic field vector). The magnetic field variables can have values,described herein as values of “magnetic field variable values” or“values of magnetic field variables.” The magnetic field variable valuescan be stationary or to can change with time. There can be any number ofmagnetic field variable values of the magnetic field variables, for anynumber of positions of the magnet at the point (or points) in space.

In some particular analyses described below, and where indicated, theterm “position” is limited to refer to a quantified geometric state ofthe magnet described along one, two, or three axes. Where indicated, theterm “orientation” refers to rotations about the one, two, or threeaxes. However, in most instances herein the term “position” refers toone or more of the above six states of the magnet.

While the position variables are described herein with up to six degreesof freedom, or dimensions (e.g., six vector elements), it will beunderstood that other coordinate systems with six or with other numbersof position variables can be used to describe a position or location.The other position variables can be mapped to the six dimensions, ornot, and the same concepts as those described herein still apply.

While the magnetic field variables are described herein with up to threedimensions (e.g., three vector elements), it will be understood thatother coordinate systems with three or with other numbers of magneticfield variables can be used to describe a magnetic field at a position.The other magnetic field variables can be mapped to the threedimensions, or not, and the same concepts as those described hereinstill apply.

As used herein, the term “processor” is used to describe an electroniccircuit that performs a function, an operation, or a sequence ofoperations. The function, operation, or sequence of operations can behard coded into the electronic circuit or soft coded by way ofinstructions held in a memory device. A “processor” can perform thefunction, operation, or sequence of operations using digital values orusing analog signals.

In some embodiments, the “processor” can be embodied in an applicationspecific integrated circuit (ASIC), which can be an analog ASIC or adigital ASIC. In some embodiments, the “processor” can be embodied in amicroprocessor with associated program memory. In some embodiments, the“processor” can be embodied in a discrete electronic circuit, which canbe an analog or digital.

As used herein, the term “module” is used to describe a “processor.”

A processor can contain internal processors or internal modules thatperform portions of the function, operation, or sequence of operationsof the processor. Similarly, a module can contain internal processors orinternal modules that perform portions of the function, operation, orsequence of operations of the module.

While electronic circuits shown in figures herein may be shown in theform of analog blocks or digital blocks, it will be understood that theanalog blocks can be replaced by digital blocks that perform the same orsimilar functions and the digital blocks can be replaced by analogblocks that perform the same or similar functions. Analog-to-digital ordigital-to-analog conversions may not be explicitly shown in thefigures, but should be understood.

As used herein, the term “predetermined,” when referring to a value orsignal, is used to refer to a value or signal that is set, or fixed, inthe factory at the time of manufacture, or by external means, e.g.,programming, thereafter. As used herein, the term “determined,” whenreferring to a value or signal, is used to refer to a value or signalthat is identified by a circuit during operation, after manufacture.

First, referring ahead to generalized FIG. 6, a magnet 600 is shown attwo physical positions 602 a, 602 b. The magnet 600 has an arbitraryshape and has a direction of magnetization described by an arrow 604.This magnet 600 is in space at a position L=(x_(M),y_(M),z_(M)) and withan orientation T=(α,β,γ), where (α,β,γ) are angles around (X,Y,Z) axis.It will be understood that x_(M), y_(M), z_(M), α, β, γ describe sixdegrees of freedom of the position of the magnet 600. In equations aboveand below, the terms L and T are together described as positionvariables.

A function, f_(M,P), can describe magnetic field values in threedimensions (x,y,z) based upon a calculation of magnetic field created bythis magnet 600, M, at any points P_(i) in space around the magnet 600,for all magnet positions/orientations (L,T). P is a matrix that containsthe coordinates of all the Pi points, i.e., in three axes, x, y, and z.The matrix containing these calculated magnetic fields (calculated by amathematical model) can be called H_(M)(P,L,T).

$\begin{matrix}{P = \begin{pmatrix}x_{1} & x_{2} & \ldots \\y_{1} & y_{2} & \ldots \\z_{1} & z_{2} & \ldots\end{pmatrix}} & (1) \\{{f_{M,P}( {L,T} )} = {H_{M}( {P,L,T} )}} & (2) \\{{H_{M}( {P,L,T} )} = \begin{pmatrix}{Hx}_{1} & {Hx}_{2} & \ldots \\{Hy}_{1} & {Hy}_{2} & \ldots \\{H\; z_{1}} & {H\; z_{2}} & \ldots\end{pmatrix}} & (3)\end{matrix}$

Thus, it should be understood that, for each point in space of themagnet, the function f_(M,P) (i.e., H_(M)(P, L, T)) uses up to sixposition variable values to describe the position of the magnet at thepoint in space, and a related three calculated magnetic field variablevalues indicative of a calculated (or predicted) magnetic field at thepoint, P, in space. There can be a direct relation between thecalculated magnetic field values and the calculated position variablevalues (position of the magnet).

In contrast, magnetic field measurements H_(mes)(P,L′,T′) can begenerated in three dimensions, (x,y,z), for example, using magneticfield sensing elements, at all the points P around the magnet 600, M, atmagnet position L′=(x′_(M),y′_(M),z′_(M)) and orientation T′(α′,β′,γ′).

Thus, it should be understood that, for each point in space of themagnet, the function H_(mes)(P,L′,T′) uses up to six position variablevalues to describe the position of the magnet at the point in space, anda related three measured magnetic field variable values indicative of ameasured magnetic field at the point, P, in space. It will also beunderstood from discussion below, that the magnetic field measurementvalues can be directly obtained from a magnetic field sensor.

Position and orientation L′ and T′ of the magnet 600, M, can bedetermined based on the three dimensional measured magnetic fieldvariable values H_(mes)(P,L′,T′), e.g., measurement made by a magneticfield sensor, and upon the three dimensional calculated magnetic fieldvariable values H_(m)(P,L,T)

To this end a distance function, d_(M,P), can be used that containsvalues of numerical distances between the three dimensional magneticfield measurements at position/orientation (L′,T′) and the threedimensional magnetic field predicted by function f_(M,P) by the abovemagnet model at position/orientation (L,T).d _(M,P)(L,T)=∥f _(M,P)(L,T)−H _(mes)(P,L′,T′)∥  (4)

The ∥ ∥ symbol stands for the Euclidean norm (or 2-norm) of a matrix. Insome embodiments, other norms can be used (1-norm or p-norm, forexample).

This function depends on the magnet M position and orientation (but alsomagnet dimensions, magnetization and material). The magnet 600 can be amoving object and the general movement can be known in advance by thesystem, at least its nominal movement characteristics.

Evaluation of the function d_(M,P) indicates how close is an up to threedimension measured magnetic field to an up to three dimension calculated(or predicted) magnetic field. Evaluated points on the distance functionare associated with up to six measured position variable values (i.e.,position of the magnet). Thus, evaluation of the function d_(M,P)ultimately indicates how close are the current evaluated (i.e.,calculated) magnet position and orientation (L,T) to the real positionand orientation of the magnet (L′,T′). Ideally, if there is unicity ofthe solution, then d_(M,P) (L,T)=0 implies that the magnet position isperfectly known.

In view of the above, a prediction of position and orientation of themagnet M can be determined by minimizing the function d_(M,P), a minimumdistance between measured and calculated magnetic such that thecurrently evaluated magnet position (Le, Te) is close to the real(actual) magnet position (L′, T′). The distance function is furtherexplained in conjunction with FIG. 7.

Note that (L_(e),T_(e)) is usually different from the real magnetposition (L′,T′) because the measurements and the magnetic model of thesystem may not be perfect.

As used herein, the term “model” as used above refers to a mathematicalfunction that takes, as input, an arbitrary magnet position andcalculates, as output, a “calculated” magnetic field that would besensed by one or more magnetic field sensing elements if the magnet wereto assume that position. The arbitrary magnet position may berepresented as one or more variables, e.g., mounting distance y andangle of rotation β in an end-of-shaft application described below inconjunction with FIGS. 1A and 1B. Thus, a magnet model may be generatedusing knowledge of the magnet's geometry and magnetic characteristics(e.g., magnetization direction and distribution), in addition to knownpositions and characteristics of the magnetic field sensing element(s)relative to the magnet. A magnet model may be generated inductively(e.g., using Maxwell equations or derivations thereof) or experimentally(e.g., by placing the magnet into many different known positions andobtaining measurements from the magnetic field sensing elements).

It will be appreciated that, from Maxwell equations and in the mostgeneral case, the field H generated by a magnetized material is given byan equation:

$\begin{matrix}{{H(P)} = {{- \frac{1}{4\pi}}{grad}{\int{\int{\int_{V}{{{M(N)} \cdot \frac{r - r^{\prime}}{{{r - r^{\prime}}}^{3}}}{dV}}}}}}} & (5)\end{matrix}$

where P is the position where the field is computed, grad is thegradient operator, M(N) is the magnetization vector at a given point Nin the magnetized material, r is the vector from the origin to P, and r′is the vector from the origin to N and dV is the differential volume.Note that H is expressed in A/m, Amperes per meter.

This equation cannot be directly computed, even in the case of verysimple magnet geometry. Thus, it is necessary to mesh the magnetgeometry into k volume elements. It is also necessary to assume thateach element of this mesh will carry a uniform magnetization.

These two assumptions lead to the simplified equation:

$\begin{matrix}{{H(P)} = {\frac{1}{4\pi}{\sum\limits_{j = 1}^{k}{\int{\int_{Sj}{{{Mj} \cdot {nj} \cdot \frac{r - {rj}}{{{r - {rj}}}^{3}}}{dS}}}}}}} & (6)\end{matrix}$

where Sj is the surface of the mesh element j, nj is the normal vectorof surface Sj, rj is the barycenter of element j, and Mj is the uniformmagnetization vector of element j. From this equation, magnet models maybe generated based on arbitrary magnet dimensions, magnetization, andposition/orientation. H(P) can indicate up to three magnetic fieldvariables (e.g., in x, y, z directions, i.e., up to three magnetic fieldvariables) associated with position variable values (e.g., with up tosix position variables).

Now referring ahead to FIG. 7, a graph 700 includes a vertical axis witha scale in units of numerical distance between calculated and measuredmagnetic fields along an X-axis (scalar values) in arbitrary units ofmagnetic field and a horizontal axis with a scale describing position ofa magnet along the X-axis in arbitrary units

A curve 702 is indicative of an illustrative distance function describedabove in conjunction with equation 4, but here the distance function isa function of only one of the position variables (of up to six positionvariables) in the dimension X and only one of the magnetic fieldvariables (of up to three magnetic field variables) in the dimension X.Points on the curve 702 are indicative of evaluations of the distancefunction at different values of the one position variable in thedimension X.

The distance function has local minima P2 and P5 at horizontal axisvalues x2 and x5 and a global minimum P4 at horizontal axis value x4. Itmay not be desirable to identify the local minima P2 and P5 at x2 andx5. Instead, it may be desirable to determine the value of the positionof the magnet only at the global minimum at x4 of the distance function702. The position x4 at the global minimum P4 of the distance function702 can be indicative of the best estimate of the magnet position alongthe X-axis.

Techniques described below in conjunction with FIGS. 4, 4A, and 4B areillustrative of a method that can find the global minimum in any numberof dimensions.

Points P1-P3 and P5-P6, or any point other than P4, are indicative ofpoints on (i.e., evaluations of) the distance function 702 at which aprocess to find the global minimum P4 of the distance function 702 atthe magnet position x4 may begin. Thus, the points P1-P3 and P5-P6 areindicative of initial distance function values, or starting distancefunction values, or approximate distance function values (and associatedposition variable values x1-x3 and x5-x6), from which the global minimumP4 of the distance function 702 at position x4 may be found, iterativelyor otherwise.

In general, it may be desirable to identify the global minimum P4 atposition x4 as rapidly as possible. For example, if the above techniquesare used to identify a rapidly moving magnet, it is desirable toidentify the global minimum rapidly. To this end, it will be understoodthat starting at the value P3 at position x3, near the global minimum,may lead to finding the global minimum P4 at position x4 more rapidlythan starting at the points P1-P2 or P5-P6. Starting at the value P3, asopposed to the values P1-P2 or P5-P6, may also lead to finding theglobal minimum P4 at position x4 rather than finding the local minima.

For clarity, the graph 700 shows a distance function in only onedimension, X. However, it should be understood that a distance functioncan be in one, two, three, four, five, or six position variabledimensions and similar local and global minima apply.

Figures below describe examples of identification of a position orlocation of a magnet with possible movement in fewer than six degrees offreedom. However, it should be understood that the same or similartechniques can be used to find a position of a magnet with one, two,three, four, five, or six degrees of freedom of movement.

Referring now to FIGS. 1, 1A, and 1B, an illustrative system 100includes a magnetic field sensor (or “sensor”) 102 proximate to a magnet104 mounted along an end of a shaft 106. The shaft 106 and magnet 104may rotate around a Y-axis 108 y of coordinate system 108 having X-axis108 x, Y-axis 108 y, and Z-axis 108 z.

The magnet 104 may have a known geometry (i.e., shape) and/ormagnetization. In the embodiment shown, the magnet 104 is aparallelepiped having a magnetization described by north and southpoles. As shown in FIG. 1A, the magnet 104 may have a magnetizationdirection 110. In some embodiments, the magnet 104 is a permanentmagnet.

As the magnet 104 rotates around the Y-axis 108 y, it has an angle ofrotation Q which may be defined relative the X-axis 108 x as shown inFIG. 1A. The magnet 104 may mounted at a distance y from sensor 102 asshown in FIG. 1B. The mounting distance y may be defined as a relativedistance along the Y-axis 108 y between a point 112 on the magneticfield sensor 102 and a point 114 on the magnet 104. The points 112, 114may be, for example, geometric centers of the magnetic field sensor 102and magnet 104, respectively.

In various embodiments, the magnetic field sensor 102 (or otherelectronic circuitry within the system 100) is configured to determinethe angle of rotation β and mounting distance y (i.e., a position orlocation of the magnet 104 in two degrees of freedom) using techniquesdescribed herein. The magnetic field sensor 102 may determine theinstantaneous distance along the Y-axis 108 y and angle of rotation β asthe shaft 106 and magnet 104 rotate.

It should be appreciated that FIGS. 1, 1A, 1B show an end-of-shaft anglesensing application with two unknown variables (β, y), wherein therelative position of the magnet 104 and magnetic field sensor 104 alongthe X-axis and Z-axis, and also rotation about the X-axis and about theZ-axis are assumed to be fixed. The unknown variables (β, y), may bereferred to as “magnet position variables” or simply “positionvariables.”

As described further below, the concepts and techniques herein can beapplied to various types of magnetic field sensing applications havingan arbitrary number of magnet position variables, e.g., one, two, three,four, five, or six (i.e., up to six) position variables that describe aposition of the magnet in up to six degrees of freedom.

Referring to FIG. 1C, in which like elements of FIGS. 1, 1B, and 1C areshown using like reference designations, a structure 120 (part ofmagnetic field sensor 102) includes four magnetic field sensing elements122 a, 122 b, 122 c, 122 d (122 generally) that may be arranged on asubstrate 124 as shown. In some embodiments, the magnetic field sensingelements 122 may be planar Hall elements having axes of maximumsensitivity perpendicular to the substrate 124 and, thus, along a Y-axisin the embodiment of FIG. 1C (the Y-axis extends into the page of FIG.1C in accordance with visible X-axis and Z-axis 108 x, 108 z).

Each of the magnetic field sensing elements 122 may provide a magneticfield measurement of the magnet 104 (FIG. 1). For a given magnetmounting distance y_(m) and angle of rotation β_(m), collectivelyreferred to as the magnet position, each of the magnetic field sensingelements 122 a, 122 b, 122 c, 122 d may provide a respective measurementB_(mes1), B_(mes2), B_(mes3), and B_(mes4) of the magnetic field Bgenerated by magnet 104. The measurements may be expressed as functionof magnet position, for example, a first sensing element 122 a may besaid to measure field B_(mes1)(y_(m), β_(m)), a second sensing element122 b to measure field B_(mes2)(y_(m), β_(m)), a third sensing element122 c to measure field B_(mes3)(y_(m),β_(m)), and a fourth sensingelement 122 d to measure a field B_(mes4)(y_(m), β_(m)).

By techniques described below, the actual magnet position (y_(m),β_(m)), which is generally unknown, may be determined using the magneticfield measurements B_(mes) and one or more models of the magnet 104 thatdescribe a calculated (i.e., predicted) magnetic field about the magnet104.

Four magnet models B_(calc1)(y,β), B_(calc2)(y,β), B_(calc3)(y,β), andB_(calc4)(y,β) may be used, each one in accordance with physicalcharacteristics (e.g., sensitivity and maximum response axis) andphysical positions of each respective magnetic field sensing element 122a, 122 b, 122 c, and 122 d. In the end-of-shaft angle sensingapplication of FIGS. 1, 1A, 1B, the magnet models may be based on theassumption that the relative position of the magnet 104 and magneticfield sensing elements 122 along the X-axis and Z-axis 108 x, 108 z androtations of the magnet about the X-axis and the Z-axis are generallyfixed. The four models B_(calc) may be similar in that they may be eachbased on the same known magnet geometry and magnetization, but maydiffer in that each is based on relative position between the magnet andone of the four different magnetic field sensing elements 122 a, 122 b,122 c, 122 d.

To determine the unknown magnet position, (y_(m), (β_(m)), anoptimization process may be used that seeks to minimize a distancefunction that is based on the magnet models B_(calc) and one or moremagnetic field measurements B_(mes). In some embodiments, rather thanusing four separate absolute measurements, the distance functioncalculates a mathematical norm of a numerical difference between avector of one or more magnetic field measurements B_(mes) and a vectorof one or more calculated magnetic fields values B_(calc).

In the embodiment of FIGS. 1 and 1A-1C, instead of absolute measurementand related absolute magnet model values, a differential magnetic fieldsensing scheme may be used to determine unknown magnet position (y_(m),β_(m)). In particular, first differential magnetic field measurementsΔ_(mes1)(y_(m), β_(m)) may be taken using the first and third sensingelements 122 a, 122 c, and second differential magnetic fieldmeasurements Δ_(mes2)(y_(m), β_(m)) may be taken using the second andfurther sensing elements 122 b, 122 d, for example, as follows:Δ_(mes1)(y _(m),β_(m))=B _(mes3)(y _(m),β_(m))−B _(mes1)(y_(m),β_(m))  (7)Δ_(mes2)(y _(m),β_(m))=B _(mes4)(y _(m),β_(m))−B _(mes2)(y_(m),β_(m))  (8)

Likewise, first differential calculated magnetic fields Δ_(calc1)(y,β)may be produced using the first and third magnet models B_(calc1),B_(calc3), and the second differential calculated magnetic fieldsΔ_(calc2)(y,β)=may be produced using the second and fourth magnet modelsB_(calc2), B_(calc4), for example, as follows:Δ_(calc1)(y,β)=B _(calc3)(y,β)−B _(calc1)(y,β)  (9)Δ_(calc2)(y,β)=B _(calc4),β)−B _(calc2)(y,β)  (10)

Using the aforementioned differential magnetic field sensing scheme, adistance function d may be defined using the differential magneticfields measurements and calculations, such as follows:

$\begin{matrix}{{d( {y,\beta} )} = {{{{\Delta_{mes}( {y_{m},\beta_{m}} )} - {\Delta_{calc}( {y,\beta} )}}} = {{\begin{matrix}{{\Delta_{{mes}\; 1}( {y_{m},\beta_{m}} )} - {\Delta_{{calc}\; 1}( {y,\beta} )}} \\{{\Delta_{{mes}\; 2}( {y_{m},\beta_{m}} )} - {\Delta_{{calc}\; 2}( {y,\beta} )}}\end{matrix}} = \sqrt{( {{\Delta_{mes}( {y_{m},\beta_{m}} )} - {\Delta_{{calc}\; 1}( {y,\beta} )}} )^{2} + ( {{\Delta_{{mes}\; 2}( {y_{m},\beta_{m}} )} - {\Delta_{{calc}\; 2}( {y,\beta} )}} )^{2}}}}} & (11)\end{matrix}$

where the symbol ∥ ∥ stands for the Euclidean norm (or 2-norm) of amatrix.

For selected magnet position variables, e.g., y and β, the distancefunction d(y,β) returns (i.e., is evaluated to be) a scalar valueindicating a how “close” the calculated differential field valuesΔ_(calc)(y,β) are to the measured differential magnetic fieldΔ_(mes)(y_(m),β_(m)). The distance function d(y,β) is minimized whenΔ_(mes1)(y_(m),β_(m))=Δ_(calc1)(y,β),Δ_(mes2)(y_(m),β_(m))=Δ_(calc2)(y,β), that is when y=y_(m) and β=β_(m)(assuming perfect magnet models and perfect measurements).

As mentioned above, an unknown magnet position (y_(m), β_(m)) may bedetermined using an optimization process that seeks to minimize thedistance function d(y,β).

In some embodiments, a minimum of the distance function d(y,β) can befound using a steepest descent principle. For example, an n-dimensionalplot (n-dimensional distance function) may be generated (where n is thenumber of unknown magnet position variables) and, starting at somechosen initialization point, an algorithm can follow the largestnegative gradient of the plot (i.e., slope in the case of a 2-D plot)and iterate until the gradient is zero.

In general, for a function ƒ of n variables in

defined as:ƒ(X) with X=(x ₁ ,x ₂ , . . . x _(n)) in

^(n)  (12)

minimizing f may include finding X_(m) such that:ƒ(X _(m))≤ƒ(X) for all X in

^(n)  (13)

It will be appreciated from FIG. 7 described above that one issue withminimization is to find a global minimum of ƒ and not a local minimum.Techniques for finding a minimum include iterative techniques (e.g.,Quasi-Newton and Simplex), but these tend to find a local minimum, ifany, and heuristic techniques (e.g., Genetic algorithm and Simulatedannealing). In various embodiments, one or more techniques describedbelow in conjunction with FIGS. 4, 4A, 4B, and 5 may be used to find aglobal minimum.

It should be appreciated that the distance function shown is a2-variable (mounting distance and angle of rotation) distance functionthat may be used to determine the position of a magnet. It will beappreciated that in other embodiments, the concepts, structures, andtechniques can be used with more than two or fewer than two magneticposition variables, e.g., any number of the six degrees of freedom. Asone example, the techniques described herein may be applied to sideshaft angle sensing applications.

The general concepts and techniques sought to be protected herein may beused with various types of magnetic field measurements includingabsolute magnetic fields measurements, differential magnetic fieldsmeasurements, and angular measurements. The magnet models may be adaptedin order to calculate, for example, the magnetic field at somepositions, the magnetic field angle at other positions and the cosine ofthe magnetic field angle at some other positions. Moreover, differenttypes of measurements may be used in combination. While mixingmeasurement types, it could be necessary to normalize each measurementand the magnet models otherwise the distance function might be dominatedby some measurements.

In some embodiments, it may be desirable to obtain at least n+1 distinctmeasurements, where n is the number of unknown magnet positionvariables. However, in some embodiments, it is possible to use ndistinct measurements, or even fewer than n distinct measurement.

In certain embodiments, the distance between magnetic field sensingelements may be selected to have a good overview of the moving magnet.In other words, for example, for a particular illustrative magnet, ifthere are four magnetic field sensing elements very close to each other,for example, 0.1 millimeters from each other, the four magnetic fieldsensing elements may sense approximately the same magnetic field. Inthis example, output signals from the four magnetic field sensingelements may be nearly the same, and thus, the information provided bythe four magnetic field sensing elements may actually be informationfrom any one of the four magnetic field sensing elements. In contrast,if the magnetic field sensing elements are further apart, for example,three millimeters from each other, the four magnetic field sensingelements may sense different magnetic fields. In this example, outputsignals from the four magnetic field sensing elements may not be thesame, and thus, the information provided by the four magnetic fieldsensing elements may be information from all four magnetic field sensingelements, which may be preferred.

While four planar Hall elements 122 a, 122 b, 122 c, 122 d are describedin FIG. 1C, in other embodiments, other types of and other quantities ofmagnetic field sensing elements can be used. For example, in oneembodiment, two planar Hall elements and two vertical Hall elements canbe used in single ended arrangements or in differential arrangements,yielding, for example, magnetic field measurement in two orthogonaldirections.

In some embodiments, to improve accuracy, it may be desirable tocompensate for magnet strength change with temperature. For example,ferrite magnet strength Br typically changes with temperature with alinear rate Δ of −0.2%/° C. (20% strength loss for a 100° C. increase oftemperature). Otherwise said, the system would need a temperature sensorand the function f_(M,P), which calculates the effect of the magnet onthe sensing elements, would take into account the temperature variation.This is easy to do since the behavior is mostly linear with temperature.For example, in equation (14) below, the magnetization M, which is knownat room temperature 20° C., can be calculated at any temperature t with:

$\begin{matrix}{{M(t)} = {{M( {20{^\circ}\mspace{14mu}{C.}} )} \cdot ( {1 + {\frac{t - 20}{100} \cdot \Delta}} )}} & (14)\end{matrix}$

It should be appreciated that either the calculated magnetic fields(i.e., model magnetic fields), the measured magnetic fields, both, orneither can be compensated to adjust for the effects of temperature.

Referring to FIGS. 2A and 2B, another illustrative system 200 includes amagnetic field sensor (or “sensor”) 202 proximate to a magnet 204. Themagnet 204 has a position (x,y,z) relative to the magnetic field sensor202, where x represents a distance along an X-axis 208 x between a point212 on the magnetic field sensor 202 and a point 214 on the magnet 204,γ represents a distance along an Y-axis 208 y between points 212 and214, and z represents a distance along an Z-axis 208 z between points212 and 214.

In some embodiments, the magnet 204 is mounted at distance z from thesensor 202 and is generally free to move about the X-Y plane (i.e., theplane formed by the X-axis and Y-axis 208 x, 208 y, respectively). Eachof the magnet position variables x, y, and z may be treated as unknownswithin the system. Because the magnet is generally free to move in theX-Y plane but is mounted along the Z-axis, it may be said that theuncertainty of both x and y positions is greater than the uncertainty ofz position.

An illustrative application that may use two dimensional linear movementis a so called “All Gear” application, in which a magnetic field sensordetects all gear selections in a manual gearbox of an automobile. Thismagnetic field sensor can detect, for example, two linear movements (orone linear and one rotation) as a gear shift lever is moved.

The magnet 204 has a known geometry and/or magnetization. In theembodiment shown, the magnet 204 is a parallelepiped having a length Mxalong the X-axis 208 x, My along the Y-axis 208 y, and Mz along theZ-axis 208 z. The magnet may have a magnetization direction 210, asshown. In one embodiment, Mx, My, and Mz are each about fifteenmillimeters.

Referring to FIG. 2C, in which like elements of FIGS. 2A and 2B areshown using like reference designations, a structure 220, part ofmagnetic field sensor 202, can include four magnetic field sensingelements 222 a, 222 b, 222 c, 222 d (222 generally) that may be arrangedon a substrate 224 as shown. A first magnetic field sensing element 222a may be arranged to have a maximum sensitivity along the X-axis 208 x,a second magnetic field sensing element 222 b to have a maximumsensitivity along the Y-axis 208 y, and third and fourth magnetic fieldsensing elements 222 c, 222 d to have maximum sensitivities along theZ-axis (the Z-axis extends out of the page of FIG. 2C). In someembodiments, first and second magnetic field sensing elements 222 a, 222b can be can be vertical Hall elements, and third and fourth magneticfield sensing elements 222 c, 222 d can be planar Hall elements. Asshown in FIG. 2C, magnetic field sensing elements 222 a, 222 c may beseparate from magnetic field sensing elements 222 d, 222 b along theX-axis 208 x by a distance D1, and magnetic field sensing elements 222a, 222 d may be separate from magnetic field sensing elements 222 c, 222b along the Y-axis 208 y by a distance D2.

Each of the magnetic field sensing elements 222 may provide a magneticfield measurement of the magnet 204. For a given magnet position(x_(m),y_(m),z_(m)), the magnetic field sensing elements 222 a, 222 b,222 c, 222 d may provide respective measurementsB_(mes1)(x_(m),y_(m),z_(m)), B_(mes2)(x_(m),y_(m),z_(m)),B_(mes3)(x_(m),y_(m),z_(m)), and B_(mes4) (x_(m),y_(m),z_(m)). Inaddition, for each sensing element 222 a, 222 b, 222 c, 222 d, arespective magnet model B_(calc1)(x,y,z), B_(calc2)(x,y,z),B_(calc3)(x,y,z), and B_(calc4)(x,y,z), i.e., predicted values ofmagnetic field, i.e., predicted magnetic field variable values indirections (x,y,z), may be based on known geometry and magnetization ofthe magnet 204, and the relative position of the sensing elements 222 tothe magnet 204.

To determine the unknown magnet position (x_(m),y_(m),z_(m)), anoptimization process may be used that seeks to minimize a distance dfunction that is based on the magnet models B_(calc) and one or moremagnetic field measurements B_(mes). In some embodiments, the distancefunction calculates a mathematical norm of a difference between a vectorof or more magnetic field measurements B_(mes) and a vector of one ormore calculated magnetic fields values B_(calc). In certain embodiments,the following distance function may be used:

$\begin{matrix}\begin{matrix}{{d( {x,y,z} )} = {{{B_{mes}( {x_{m},y_{m},z_{m}} )} - {B_{calc}( {x,y,z} )}}}} \\{= {\begin{matrix}\begin{matrix}{{B_{{mes}\; 1}( {x_{m},y_{m},z_{m}} )} - {B_{{calc}\; 1}( {x,y,z} )}} \\\vdots\end{matrix} \\{{B_{{mes}\; 4}( {x_{m},y_{m},z_{m}} )} - {B_{{calc}\; 4}( {x,y,z} )}}\end{matrix}}}\end{matrix} & (15) \\{\mspace{101mu}{= \sqrt{\begin{matrix}\begin{matrix}{( {{B_{{mes}\; 1}( {x_{m},y_{m},z_{m}} )} - {B_{{calc}\; 1}( {x,y,z} )}} )^{2} +} \\{( {{B_{{mes}\; 2}( {x_{m},y_{m},z_{m}} )} - {B_{{calc}\; 2}( {x,y,z} )}} )^{2} + \ldots +}\end{matrix} \\( {{B_{{mes}\; 4}( {x_{m},y_{m},z_{m}} )} - {B_{{calc}\; 4}( {x,y,z} )}} )^{2}\end{matrix}}}} & (16)\end{matrix}$

As described above, it should be appreciated that evaluation of the3-variable distance function returns a scalar value. The combination ofmagnetic field variable values (x,y,z) that minimizes and evaluation ofthe distance function d may be used as a prediction of the actual magnetposition (x_(m),y_(m),z_(m)). In some embodiments, the range of one ormore position variable values x, y, z may be selected based uponoperating assumptions. For example, it may be assumed that the magnetposition may change +/−1 mm along X-axis and Y-axis 208 x, 208 y (i.e.,x_(m) and y_(m) may have a range [−11 mm, 11 mm]) and that the magnetmounting position may vary between 6 mm and 8 mm along the Z-axis 208 z(i.e., z_(m) may have a range [6 mm, 8 mm])

In other embodiments, other ranges may be assumed.

Referring now to FIG. 3, an illustrative magnetic field sensor 300 caninclude one or more magnetic field sensing elements 302 coupled insingle ended (absolute) or differential arrangements. The one or moremagnetic field sensing elements 302 can generate one or more magneticfield signals 302 a, which can be single ended (absolute) ordifferential signals.

The magnetic field signal 302 a can be received by an analog-to-digitalconverter 304 to generate a converted signal 304 a.

A module 316 can be coupled to the converted signal 304 a.

A memory device 310 can include a plurality of stored values. Some ofthe stored values can describe a sensed magnet in a particular way,e.g., a sensed magnet geometry and physics, referred to herein as valuesA.

In some embodiments, the stored values can describe the sensed magnet ina different way, e.g., calculated (or predicted) magnetic fieldvariable, f_(M,P), calculated at a plurality of possible positions ofthe magnet, referred to herein as values B.

In some embodiments, the stored values can describe the sensed magnet ina different way, e.g., pre-measured magnetic field variable values,Hmeas, measured at a plurality of possible positions of the magnet,measured during or before production of the magnetic field sensor 300,and referred to herein as values C.

Some other ones of the stored values can describe the magnetic fieldsensing element(s) 302 in a particular way, e.g., types, sensitivity,temperature coefficient (e.g., sensitivity change with temperature), andphysical positions of the magnetic field sensing element(s) 302,referred to herein as values D.

In some embodiments, the module 316 can also be coupled to receivestored values 310 b, e.g., values D above, that describe the magneticfield sensing element(s) 302. The module 316 can be operable to generateone or more measured magnetic field variable values, Hmeas, e.g., in upto three dimensions. In some embodiments, the one or more measuredmagnetic field variable values can be temperature compensated by themodule 316 in accordance with the received stored values 310 b thatdescribe the magnetic field sensing element(s) 302.

A module 312 can receive stored values 310 a, values A, B, or C, thatdescribe the sensed magnet and can receive the stored values 310 b,values D, that describe the magnetic field sensing element(s) 302.

In some embodiments that use values A or B described above, using amodel, for example, Maxwell equation approximations described above,e.g., in equation (6), the module 312 can be operable to generatemagnetic field variable values, f_(M,P), that describe expected magneticfields around the magnet in up to three dimensions, and in the one ormore of the six degrees of relative motion of the magnet relative to themagnetic field sensing elements 302. In some embodiments, the one ormore calculated magnetic field variable values can be temperaturecompensated by the module 312 in accordance with the received storedvalues 310 b that describe the magnetic field sensing element(s) 302.

In some alternate embodiments that use values C described above, themagnetic field variable values that describe the magnet arepre-calculated as values 310 a, f_(M,P), which are directly received bythe module 312, in which case, only temperature compensation may be doneby the module 312, and predictions by the model need not be done in themagnetic field sensor 300.

A module 314 can receive calculated magnetic field variable values 312 aaround the sensed magnet and can receive the measured magnetic fieldvariable values, Hmeas, β16 a at the present position of the sensedmagnet. The calculated magnetic field variable values 312 a can beassociated with the measured magnetic field variable values 316 a, i.e.,the values 312 a of the calculated magnetic field variables (x, y, z, α,β, γ) retrieved from the module 312 can have one or more of the measuredmagnetic field variable values 316 a of the measured magnetic fieldvariables (x,y,z).

The module 314 can calculate an initial or approximate value of adistance function, for example, P3 of 702 FIG. 7 and an initial orapproximate value of one or more position variables, e.g., x3 of FIG. 7.The module 314 can provide as an output 314 a, the initial orapproximate value of the one or more position variables. FIGS. 4A and 4Bdescribe illustrative techniques to generate the initial or approximatevalue of one or more position variables 314 a. To this end, the module314 may use calls to and returned values from (represented by arrow 318b) a distance function module 318 to identify the initial or toapproximate distance function value (e.g., P3 of FIG. 7) andcorresponding initial or one or more approximate position variablevalues (e.g., x3 of FIG. 7).

The module 318 can be coupled to the measured magnetic field variablevalues 316 a, Hmeas, and to the calculated magnetic field variablevalues 312 a, f_(M,P), and can return a distance function scalar value,(represented by arrow 318 a). Individual points on the curve 702 of FIG.7 show an example of scalar values, P, of a distance function andassociated values of a position variable, x, with one degree of freedom.

A module 320 coupled to receive the scalar distance function values 318a, (e.g., points on curve 702 of FIG. 7), coupled to receive the initialor approximate position variable values 314 a (e.g., x3 of FIG. 7), cangenerate a global minimum of the distance function, and can return anestimated or actual position 320 a, in up to six degrees of freedom, ofthe sensed magnet (not shown) (e.g., at x4 of FIG. 7) proximate to themagnetic field sensor 300.

A diagnostic module 324 can be coupled to the one or more magnetic fieldsensing elements 302 and/or to the module 305 and can generatediagnostic information 324 a.

An output module 322 can combine the estimated or actual magnet positionvariable value 320 a with the diagnostic information 324 a and cangenerate and output signal indicative of the actual magnet position andindicative of the diagnostic information. However, in some embodiments,the diagnostic module 324 and the diagnostic information 324 a are notprovided.

In some embodiments, the magnetic field sensor 300 can include atemperature sensor 306 to generate a temperature signal indicative of atemperature of the magnetic field sensor. An analog-to-digital converter308 can be couple to the temperature signal and can generate a convertedtemperature signal 308 a.

The converted temperature signal 308 a can be provided to one of, orboth of, the modules 312, 316. With a converted temperature signal 308a, one of, or both of, the modules 312, β16 can compensate forsensitivity effect of temperature upon the one or more magnetic fieldsensing elements 302 or upon the model of module 312, for example, usingthe equation (14) above.

In some embodiments, the module 314 is not used and initial orapproximate position variable values 314 a are not used. Theseembodiments may be well suited for systems in which the distancefunction has only a global minimum and no local minimum. Instead, themodule 320 a finds a minimum of a distance function, and thecorresponding magnet position, with a pre-calculated starting point.

In other embodiments, the module 320 is not used. Instead, theapproximate position variable value(s) 314 a are directly sent to theoutput module 322. These embodiments may be well suited for systemswhere very high speed of movement of the sensed magnet is necessary.

FIGS. 4, 4A, 4B, and 5 are flow diagrams showing illustrative processingthat can be implemented within, for example, the magnetic field sensor300 of FIG. 3. Rectangular elements (typified by element 402 in FIG. 4),herein denoted “processing blocks,” represent computer softwareinstructions or groups of instructions. Diamond shaped elements(typified by element 502 in FIG. 5), herein denoted “decision blocks,”represent computer software instructions, or groups of instructions,which affect the execution of the computer software instructionsrepresented by the processing blocks.

Alternatively, the processing and decision blocks may represent stepsperformed by functionally equivalent circuits such as a digital signalprocessor (DSP) circuit or an application specific integrated circuit(ASIC). The flow diagrams do not depict the syntax of any particularprogramming language but rather illustrate the functional informationone of ordinary skill in the art requires to fabricate circuits or togenerate computer software to perform the processing required of theparticular apparatus. It should be noted that many routine programelements, such as initialization of loops and variables and the use oftemporary variables may be omitted for clarity. The particular sequenceof blocks described is illustrative only and can be varied withoutdeparting from the spirit of the concepts, structures, and techniquessought to be protected herein. Thus, unless otherwise stated, the blocksdescribed below are unordered meaning that, when possible, the functionsrepresented by the blocks can be performed in any convenient ordesirable order.

Referring now to FIG. 4, a process begins at block 402, where one ormore magnetic field measurements proximate to a magnet are obtainedusing one of more magnetic field sensing elements, for example, the oneor more magnetic field sensing elements 302 of FIG. 3. As describedabove, the magnetic field measurement can be differential measurements,each measurement taken as a difference of measurement by two magneticfield sensors, or single ended measurements for which each magneticfield measurement is taken by a separate respective magnetic fieldsensing element. These measurements result in the above-describedmeasured magnetic field variables values 316 a of FIG. 3 of at least oneof the measure magnetic field variable (x,y,z)

At block 404 calculated magnetic fields are determined using a model ofthe sensed magnet. These calculations result in the above-describedcalculated magnetic field variables 312 a of FIG. 3. As described abovein conjunction with FIG. 3 the calculated magnetic field variable valuescan be calculated and stored in advance or can be calculated duringoperation of the magnetic field sensor.

At block 406, initial values of one or more position variablesassociated with the sensed magnet are determined, for example, inaccordance with FIG. 4A or 4B. See also blocks 312 and 314 of FIG. 3.Block 406 can call the calculated magnetic field variable values (seedashed lines) from block 404 in accordance with the measured magneticfield variable values measured at block 402.

At block 408, an optimization process is performed to determineoptimized values of the position variables initialized at block 406, forexample, in block 320 of FIG. 3. The optimization process minimizes adistance function, which corresponds to the optimized values of theposition variables. The optimization process can be initialized with theinitial values of the corresponding position variables according tovalues 314 a of FIG. 3. The distance function can use (e.g., can call,see dashed lines) the calculated magnetic field variable values (e.g.,the values 312 a of FIG. 3), calculated or obtained at block 404, andcan use the magnetic field measurements (e.g., the values 316 a of FIG.3) of block 402, and minimizes a numerical distance between the modeland the measurements.

At block 410, the process 400 returns an estimated or actual position ofthe sensed magnet, e.g., one or more associated position variablevalues.

Two methods of generating the initial values of position variables atblock 406 are described below in conjunction with FIGS. 4A and 4B.However, these are only two methods that can be used to find the initialor approximate position variable values. In some embodiments the initialvalues of position variables can be any values in the range of positionvariable values, (see, e.g., x1 and x6 of FIG. 3).

As described above, in some embodiments, block 406 is eliminated. Inother embodiments, the optimization of block 408 does not use theinitial position variable values of block 406.

Referring now to FIG. 4A, in a process 420, also referred to herein as a“brute force” method of finding the initial or approximate positionvariable values, begins at block 422.

At the block 422, of a plurality of position variable values can be usedwith the model of the magnet to describe magnetic fields around thesensed magnet, the position variable values are discretized into rangesof values. The discretized position variable values are associated withdiscretized calculated magnetic field variable values. The discretizedposition variable values can be reduced in range(s), or can simply bemore granular than resolution of position variable values otherwisedesired for the application. The discretized position variable valuescan be described as a grid of calculated and discretized positionvariable values.

At block 424, using the grid of calculated and discretized positionvariable values, using a model of the field generated by the sensedmagnet (calculated magnetic field variable values at associateddiscretized position variable values), and using the measured magneticfield (measured magnetic field variable values) measured by the one ormore magnetic field sensing elements of block 302 of FIG. 3, a minimumof a discretized distance function can be calculated. The minimum of thediscretized distance function can be associated with initial orapproximate discretized position variable values.

At block 426, the initial or approximate position variable values can bereturned to the main function 400.

The above brute force method finds an approximate global minimum of thedistance function d_(M,P) by brute force, corresponding to theapproximate position (L_(a),T_(a)) of the magnet, and can thereafterrefine this approximate minimum with, for example, a fast iterativeoptimization algorithm (like simplex) starting at (L_(a), T_(a)). Thiswill return the evaluated magnet position (L_(e),T_(e)) (see block 410).In order to find (L_(a),T_(a)), up to six dimensions space

⁶ can be discretized in all dimensions (discretization can be differentfor each one of the six dimensions and not necessarily uniform). Itgives a six dimensions grid G. The distance function d_(M,P) is thenevaluated on all points of this grid G. The approximate global minimumcorresponds to the point (L_(a),T_(a)) such that d_(M,P) (L_(a),T_(a))is a minimum on the grid.

In a non-limiting example of the method of FIG. 4, and referring toFIGS. 2, 2A, 2B, 2C, first the method 420 discretizes the 3D space (only3D because (α,β,γ) are known) and creates the grid G: For example, Xdirection can be discretized with a 2.5 millimeter step size, Ydirection can be discretized with a 2.4 millimeter step size and Zdirection can be discretized with a 0.6 millimeter step size.

Then, the distance function, d_(M,P), on this grid G can be calculated.For example, the minimum can be L_(a)=(−2.6, 3.6, −2.8) expressed inmillimeters. The above can be an approximate global minimum which isused as a starting point of an iterative algorithm.

Now, using, for example, a simplex minimization algorithm on the threeposition variables (x,y,z) and the position corresponding to theapproximate global minimum of the distance function described above asthe starting point, another global minimum of a non-discretized distancefunction can be calculated, for example, in FIG. 4, to determine aposition, e.g., (x_(M),y_(M),z_(M))=(−1.99, 3.01, −2.51) of a sensedmagnet (where α,β,γ are fixed).

The system accuracy can be evaluated on a full movement range of themagnet. Inaccuracies can be larger on the edges of the movement rangebecause field strength is lower at these positions and, consequently,the measurement inaccuracies tend to make the detection more difficult.

Accuracy could be improved using more field measurements or astronger/larger magnet, for example.

If the above discretization (grid) is not fine enough, the minimumreturned by the initial brute force search might be close to a localminimum. On the other hand, if the discretization is too fine, then thebrute force evaluation may require a lot of calculations and may consumetime. Consequently, a compromise needs to be found, which depends on thecomputation capability, the response time required by the applicationand the application itself. For example: a good knowledge of theapplication can tell you approximately: (1) how many minima to expect(local and global), (2) where are the minima, and (3) if all the 6dimensions are required. In some illustrative applications describedabove, only two dimensions may be used (the other degrees of freedom arefixed and known).

Referring now to FIG. 4B, in a process 440, also referred to herein as a“limited range” method of finding the initial or approximate positionvariable values, begins at block 442.

At the block 442, of a plurality of position variables in six dimensionsthat can be used with the model of the magnet to describe the sensedmagnet position, partition the plurality of position variables intofirst, second, and third position variables. The first positionvariables can include some (e.g., three) position variables of the sixposition variables that are fixed in value, the second positionvariables can include other position variables (e.g., two) that describefull motion of the magnet, and the third position variables can includestill other position variables (e.g., one) that describes limited rangesof motion of the magnet.

At block 444, using measured magnetic fields measured by the one or moremagnetic field sensing elements of blocks 302 and 316 of FIG. 3, andusing calculated magnetic fields calculated by the above-described modelof block 312 of FIG. 3, generate a minimum of a distance function andassociated initial position variable values of the second group whileholding position variable values of first and third groups to be fixed.The initial or approximate distance function value is associated with orcorresponds to initial or approximate position variable values of thesecond position variable group.

At block 446, the process 440 returns the initial or approximate valuesof the first, second, and third position variables identified forexample, in block 406 of FIG. 4 and as described, for example in block314 of FIG. 3.

The limited range method described above is useful when some positionvariables have very limited range compared to other variables. A usefulexample has a range of position variable values that is ten timessmaller than others of the position variable values. V_(L) can be agroup of position variables with limited range and V_(N) can be a groupof position variables with large range. First, an iterative algorithmcan be used to minimize a distance function d_(M,P), limited to thecorresponding to position variables V_(N) and with the variables V_(L)fixed to their nominal positions. The starting point of the optimizationcould be any points in the range of V_(N) variables. This will lead to afirst approximate position (L_(a),T_(a)), corresponding to anapproximate minimum of the distance function. Second, the iterativealgorithm can be used again to minimize a distance function, d_(M,P),but starting at (L_(a),T_(a)), and on all the magnetic field variablesin order to find the global minimum (L_(e),T_(e)).

While three types of (i.e., groups of) position variables are describedabove, in some embodiments, only the first and second, or the first andthird position variables are used and the missing type is not used or isheld fixed.

Note that, in a real application, if the calculation rate of themagnetic field sensor 300 of FIG. 3 is much faster than the magnetmovement speed, then once the global minimum has been found thanks toone of the above algorithms (from FIG. 4A or FIG. 4B), it is notnecessary anymore to use these above algorithms. Indeed, the iterativealgorithm could simply be used with a starting point being the lastevaluated magnet position.

In some embodiments, such as that described below in conjunction withFIG. 5, a procedure like those described above in conjunction with FIGS.4A and 4B is only done once, or a few times, for example, at startup ofthe magnetic field sensor 300 or at startup of movement of a sensedmagnet. In these embodiments, when the sensor is started, the positionof the magnet is totally unknown, so the magnet position evaluationstarts with the “brute force” method of FIG. 4A or “limited range”method of FIG. 4B in order to find initial or approximate position(i.e., position variable values). After this is done the first time, ina second part, the magnet position can be evaluated using a classicaliterative minimization algorithm which is initialized with a previouslycalculated magnet position (i.e., position variable values). The secondpart described above can be referred to herein as a “tracking” method.

Referring now to FIG. 5, and in accordance with comments above, anillustrative process 500 begins at block 502, where it is determined ifa previously evaluated position variable values have been evaluated.

If at block 502, previously evaluated position variable values areavailable then the method 500 proceed to block 506, where, in someembodiments, the previously evaluated position variable values can beused as initial or approximate position variable values.

At block 508, an optimization process can be used to find a globalminimum of the distance function the same as or similar to block 408 ofFIG. 4.

At block 510, the process 500 returns evaluated magnet position variablevalues.

If, at block 502, there are not previously evaluated position variablevalues available, then the method 500 continues to block 504, where aninitial or approximate position variable values are calculated, forexample, using the process of FIG. 4A or 4B.

The process then continues to block 508.

This tracking method 500 above can reduce computing time. The trackingmethod avoid a continual need for finding initial or approximateposition variable values using the “brute force” method or “limitedrange” method for each position evaluation.

All references cited herein are hereby incorporated herein by referencein their entirety.

Having described certain embodiments, which serve to illustrate variousconcepts, structures, and techniques sought to be protected herein, itwill be apparent to those of ordinary skill in the art that otherembodiments incorporating these concepts, structures, and techniques maybe used. Elements of different embodiments described hereinabove may becombined to form other embodiments not specifically set forth above and,further, elements described in the context of a single embodiment may beprovided separately or in any suitable sub-combination. Accordingly, itis submitted that the scope of protection sought herein should not belimited to the described embodiments but rather should be limited onlyby the spirit and scope of the following claims.

What is claimed is:
 1. A method of determining a position of a magnet,the position identified by one or more position variables, the methodcomprises: generating one or more magnetic field measurements of themagnet and an associated one or more measured magnetic field variablevalues using one or more magnetic field sensing elements, wherein theone or more magnetic field sensing elements includes first and secondmagnetic field sensing elements most responsive to magnetic fields alonga first axis, a third magnetic field sensing element most responsive tomagnetic fields along a second axis, and a fourth magnetic field sensingelement most responsive to magnetic fields along a third axis;identifying calculated magnetic field variable values associated with aplurality of positions of the magnet, wherein the identifying thecalculated magnetic field values comprises using a mathematical model tocalculate a respective magnetic field expected at each of the one ormore magnetic field sensing elements at a plurality of positions of themagnet; performing an optimization process to determine a minimal valueof a distance function, wherein the distance function calculates atleast one difference between the calculated magnetic field variablevalues at positions of the one or more magnetic field sensing elementsand the one or more measured magnetic field variable values, wherein theoptimization process searches for the minimal value of the distancefunction based on the calculated at least one difference; anddetermining the position of the magnet by associating the minimal valueof the distance function with corresponding values of the one or moreposition variables.
 2. The method of claim 1, wherein the one or moreposition variables includes an angle of rotation of the magnet around afirst axis.
 3. The method of claim 2, wherein the one or more magneticfield sensing elements include at least two magnetic field sensingelements most responsive to magnetic fields along the first axis.
 4. Themethod of claim 1, wherein the one or more magnetic field sensingelements are arranged to generate at least one differential measurementof the magnetic fields.
 5. The method of claim 1, wherein the one ormore position variables include a position of the magnet along a firstaxis and a position of the magnet along a second axis.
 6. The method ofclaim 1, further comprising: determining initial values of the one ormore position variables, wherein the optimization process is initializedwith the initial values of the one or more position variables.
 7. Themethod of claim 6, wherein determining the initial values of the one ormore position variables comprises: discretizing ranges of values ofselected ones of the one or more position variables to generate aplurality of discretized position variable values; identifying a minimumnumerical distance between the calculated magnetic field variable valuesat positions of the one or more magnetic field sensing elements for onesof the plurality of discretized position variable values and the one ormore measured magnetic field variable values identifying the initialvalues of the one or more position variables in accordance with theminimum numerical distance.
 8. The method of claim 6, wherein thedetermining the initial values of the one or more position variablescomprises: partitioning the one or more position variables into one ormore first position variables and one or more second position variables;and identifying a minimum numerical distance between the calculatedmagnetic field variable values for the one or more second positionvariables while holding values of the one or more first positionvariables fixed; and identifying the initial values of the one or moreposition variables in accordance with the minimum numerical distance. 9.The method of claim 8, wherein at least one of the one or more firstposition variables has a smaller range than another one of the one ormore first position variables.
 10. The method of claim 1, where the oneor more magnetic field measurements comprises two magnetic fieldmeasurements, and wherein the two magnetic field measurement arecombined together to generate a differential magnetic field measurement.11. The method of claim 1, further comprising: determining initialvalues of the one or more position variables; during a first timeperiod, using the initial values of the one or more position variablesto find an associated one or more optimized position variable valuesduring the optimizing; and during a second time period time period afterthe first time period, using the one or more optimized position variablevalues to find another optimized one or more position variable valuesduring the optimizing.